This application discloses subject matter similar to subject matter disclosed in U.S. patent application Ser. No. 09/912,065, filed on Jul. 25, 2001.
The present invention relates to thermally stable, high coercivity, high area density, patterned magnetic recording media, and to a method for manufacturing same. The invention has particular applicability in the fabrication of thermally stable, high areal density media with integrally formed servo patterns.
Thin film magnetic recording media, e.g., in hard disk form, are conventionally employed for storing large amounts of data/information in magnetizable form. Referring now to FIG. 1, shown therein, in simplified, schematic cross-sectional view, is a portion of a dual-sided, thin-film magnetic disk medium 1 of the type contemplated by the present invention, comprising a substantially rigid, non-magnetic substrate 10, typically comprised of an aluminum (Al) alloy, e.g., Alxe2x80x94Mg. Alternative materials for use as substrate 10 include glass, ceramics, glass-ceramics composites and laminates, polymers, and other non-magnetic metals and alloys. Al-based substrate 10 is provided, in sequence, at both major surfaces, with a polished and/or textured amorphous Ni-P underlayer 12, a polycrystalline seed layer 14, typically a Cr-based layer deposited by sputtering, a magnetic layer 16 comprised of a ferromagnetic material, e.g., an oxide or a Co-based alloy, a protective overcoat layer 18, typically of a diamond-like carbon (DLC) material, and a lubricant topcoat layer 20, e.g., of a fluorine-containing polymer.
Adverting to FIG. 2, shown therein, in simplified, schematic plan view, is a magnetic recording disk 30 having a data zone 34 including a plurality of servo tracks, and a contact start/stop (CSS) zone 32. A servo pattern 40 is formed within the data zone 34, and includes a number of data track zones 38 separated by servo tracking zones 36. The data storage function of disk 30 is confined to the data track zones 38, while servo tracking zones 36 provide information to the disk drive which allows a read/write head to maintain alignment on the individual, tightly-spaced data tracks.
Although only a relatively few of the servo tracking zones are shown in FIG. 2 for illustrative simplicity, it should be recognized that the track patterns of the media contemplated herein may include several hundreds of servo zones to improve head tracking during each rotation of the disk. In addition, the servo tracking zones need not be straight radial zones as shown in the figure, but may instead comprise arcs, intermittent zones, or irregularly-shaped zones separating individual data tracks.
In operation of such disk-type media, a typical contact start/stop (CSS) method involves use of a floating transducer head gliding at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surfaces of the transducer head and the disk. During reading and recording (writing) operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the transducer head can be freely moved in both the circumferential and radial directions, thereby allowing data to be recorded and retrieved from the disk at a desired position in a data zone.
In conventional hard disk drives, data is stored in terms of bits along the data tracks. In operation, the disk is rotated at a relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which radially positions the head on the disk surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disk, i.e., over a data track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above that track. By moving the actuator arm, the magnetic head assembly is moved radially on the disk surface between tracks. Many actuator arms are rotatable, wherein the magnetic head assembly is moved between tracks by activating a servomotor which pivots the actuator arm about an axis of rotation. Alternatively, a linear actuator may be used to move a magnetic head assembly radially inwardly or outwardly along a straight line.
To record information on the disk, the transducer creates a highly concentrated magnetic field in close proximity to the magnetic recording medium. During writing, the strength of the concentrated magnetic field directly under the write transducer is greater than the coercivity of the recording medium, and grains of the recording medium at that location are magnetized in a direction which matches the direction of the applied magnetic field. The grains of the recording medium retain their magnetization after the magnetic field is removed. As the disk rotates, the direction of the writing magnetic field is alternated, based on bits of the information being stored, thereby recording a magnetic pattern on the track directly under the write transducer.
On each track, eight xe2x80x9cbitsxe2x80x9d typically form one xe2x80x9cbytexe2x80x9d and bytes of data are grouped as sectors. Reading or writing a sector requires knowledge of the physical location of the data in the data zone so that the servo-controller of the disk drive can accurately position the read/write head in the correct location at the correct time. Most disk drives use disks with embedded xe2x80x9cservo patternsxe2x80x9d of magnetically readable information. The servo patterns are read by the magnetic head assembly to inform the disk drive of track location. In conventional disk drives, tracks typically include both data sectors and servo patterns and each servo pattern typically includes radial indexing information, as well as a xe2x80x9cservo burstxe2x80x9d. A servo burst is a centering pattern to precisely position the head over the center of the track. Because of the locational precision needed, writing of servo patterns requires expensive servo-pattern writing equipment and is a time consuming process.
A conventional approach to the servo-sensing problem comprises the use of mechanical voids or depressions in the magnetic layer between tracks formed by stamping or otherwise physically marking a pattern on the disk to function as servo patterns. A magnetic material layer is then applied at a constant thickness over the entire disk surface. When this type of disk is used, the distance from the magnetic head to magnetic material in the depressions is further than the distance from the magnetic head to magnetic material in the data track. The increased distance both reduces the strength of the signal from the depressions and reduces the contribution from the depressions to the magnetic field sensed by the read/write head.
While the depressions or voids formed in the disk are helpful in increasing track density, they tend to reduce the tribological performance of the disk assembly. For example, during operation of the magnetic recording medium, the slider no longer travels over a smooth surface and thus causes several mechanical performance drawbacks. These drawbacks include modulation of fly height when encountering servo patterns, fly height perturbations due to topographical changes from the track width definition, glide defects from the stamping process, and disk distortion due to the servo patterning process. Therefore, it is considered preferable to provide the servo pattern without incurring variations in surface topography.
Several approaches to forming servo-patterns are disclosed in the prior art. For example, U.S. Pat. No. 6,153,281 and U.S. Pat. No. 5,858,474, both to Meyer et al., disclose a magnetic medium having permanently defined boundaries between data tracks and a constant surface smoothness. The servo-patterns may be formed, at least in part, by a variety of techniques including, inter alia, laser ablation, laser heating, photolithography, deposition, ion milling, reverse sputtering, ion implantation, etc., which techniques and can be utilized individually or in combination, with either the magnetic layer or underlayer, to create relatively non-magnetic areas. U.S. Pat. Nos. No. 6,086,961 and U.S. Pat. No. 5,991,104, both to Bonyhard, disclose creating non-magnetic areas in the formation of servo-sensing patterns by ion implantation, where the ion implantation destroys or alters the magnetic properties of the magnetic layer.
Still other methods for forming servo-patterns are known in the prior art. For example, U.S. Pat. No. 6,055,139 to Ohtsuka et al. discloses implanting a magnetic hard disk with chromium ions to change regions of the magnetic layer into non-magnetic regions. U.S. Pat. No. 4,556,597 to Best et al. discloses providing a magnetic recording disk substrate with a capacitive servo-pattern formed by implanting dopant species into the substrate to modify the conductivity thereof. U.K. Pat. 1,443,248 to Sargunar discloses magnetic recording media and fabrication methods therefor by forming low coercivity regions therein by implantation of chromium ions. However, it is believed that the use of such metal ions adversely affects the magnetic layer.
Commonly assigned, co-pending U.S. patent application Ser. No. 09/912,065, filed Jul. 25, 2001, by the present inventors, the entire disclosure of which is incorporated herein by reference, discloses an improved method for forming servo patterns in high areal density, thin film magnetic recording media, without incurring variations or changes in media surface topography, and servo-patterned thin film magnetic recording media obtained thereby, in which nitrogen ions or heavier ions of at least one inert gas having an atomic weight of at least 35 (e.g., Ar ions) are selectively implanted (at appropriate dosages and energies) into regions of a thin film magnetic recording layer exposed through a pattern of openings in an apertured mask (e.g., in the form of a stencil or resist layer) overlying the surface of the magnetic recording layer, the pattern of openings in the apertured mask corresponding to a desired servo pattern of lower coercivity regions to be formed in the magnetic layer, whereby, for example, the coercivity (Hc) and magnetic remanence-thickness product (Mrt) of the ion-implanted regions can be controllably and reproducibly reduced by a desired amount. For example, implantation of argon ions at appropriate dosages and energies can reduce an initial value of Hc which is as high as about 4,000 Oe, to as low as about 200 Oe and reduce an initial value of Mrt of which is as high as about 0.40, to as low as about 0.15 memu.; whereas implantation of nitrogen ions generally results in smaller reductions in Hc and Mrt values.
However, when the reduction in Hc and Mrt incurred by the ion-implanted regions according to the above methodology is substantial, e.g., as in the case of argon ion implantation at certain dosages and energy levels, significant concerns are raised relating to the thermal stability of the implanted media. In this regard, a fine balance must be achieved between thermal decay, signal-to-noise ratio (SNR), and writability. As a consequence, advanced magnetic media fabricated according to the above-described ion implantation methodology must have an adequate margin of thermal stability. However, because the ion-implanted regions may have substantially lower Hc and Mrt values than the non-implanted regions, the former-type regions may have substantially and significantly lower thermal stability than the latter-type regions, which may, in turn, result in long-term problems such as thermal decay in signal amplitude. The substantially lower values of Mrt may also yield a lower amplitude of the magnetic transition signal, further adversely affecting SNR for the ion implantation-induced magnetic transition.
In view of the above, there exists a need for methodology and instrumentalities for performing servo patterning of thin film, high areal density, magnetic recording media, which are free of the above-stated concerns and difficulties relating to poor, or reduced, thermal stability of the ion-implanted regions constituting the servo and data track patterns of such media. Moreover, there exists a need for methods and instrumentalities for performing rapid, cost-effective servo patterning of thin film, high areal density magnetic recording media which methods and instrumentalities do not engender the above-stated concerns and are fully compatible with the requirements of automated magnetic hard disk manufacturing technology.
The present invention addresses and solves the above-described problems and disadvantages associated with ion implantation of thin film magnetic recording media for servo pattern formation therein, due to reduction in, or loss of, thermal stability and/or signal amplitude, arising from performing ion implantation for servo pattern creation, while maintaining full compatibility with all aspects of conventional automated ion implantation technology and methodology.
An advantage of the present invention is an improved method of making a servo-patterned magnetic recording medium.
Another advantage of the present invention is an improved method of manufacturing a servo-patterned magnetic recording medium without affecting surface topography of the medium and maintaining good thermal stability and magnetic performance characteristics.
Still another advantage of the present invention is an improved, servo-patterned magnetic recording medium.
Yet another advantage of the present invention is an improved, servo-patterned magnetic recording medium having substantially uniform surface topography while exhibiting good thermal stability and magnetic performance characteristics.
Additional advantages and other aspects and features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a method of making a servo-patterned magnetic recording medium, which method comprises the sequential steps of:
(a) providing a magnetic recording medium, the medium including a magnetic layer having preselected first, higher values of magnetic coercivity Hc and magnetic remanence-thickness product Mrt;
(b) providing an apertured mask overlying a surface of the magnetic recording medium, the apertured mask including a plurality of servo pattern openings extending therethrough for selectively exposing a plurality of surface areas of the magnetic recording medium corresponding to the servo pattern;
(c) bombarding the apertured mask with ions for implanting the ions into the plurality of exposed surface areas of the magnetic recording medium for selectively reducing the first, higher values of Hc and Mrt of the magnetic layer at the exposed surface areas to preselected second, lower values of Hc and Mrt; wherein:
step (a) comprises providing a magnetic recording medium including a magnetic layer having sufficiently high first values of Hc and Mrt such that step (c) provides each of the plurality of exposed, ion-implanted surface areas of the magnetic layer with second, lower values of Hc and Mrt which are sufficiently lower than the first, higher values of Hc and Mrt for functioning as servo pattern-defining areas, but sufficiently high for providing the medium with thermal stability, high amplitude of magnetic transition, and high signal-to-noise ratio (SNR).
In accordance with certain exemplary embodiments of the present invention, step (a) comprises providing a magnetic recording medium wherein the preselected first, higher values of Hc and Mrt are in the range from about 6,500 to about 10,000 Oe and in the range from about 0.55 to about 0.60 memu, respectively; and step (c) comprises bombarding the apertured mask to form ion-implanted areas of the magnetic layer having preselected, second, lower values of Hc and Mrt of about 6,000 Oe and about 0.50 memu, respectively.
According to other embodiments of the present invention, step (a) comprises providing a magnetic recording medium wherein the preselected first, higher values of Hc and Mrt are about 6,000 Oe and 0.50 memu, respectively; and step (c) comprises forming ion implanted areas having preselected, second, lower values of Hc and Mrt of about 4,000 Oe and 0.40 memu, respectively.
According to other particular embodiments of the invention, step (c) comprises bombarding the apertured mask with ions selected from the group consisting of nitrogen ions and ions of at least one rare gas element having an atomic weight of at least 35. Embodiments of the invention comprise bombarding the apertured mask with nitrogen or argon ions at a dosage of from about 1xc3x971010 to about 1xc3x971020 ions/cm2 and an energy of from about 5 to about 150 KeV.
According to embodiments of the present invention, step (b) comprises providing an apertured mask including a plurality of openings for providing the magnetic layer with a data zone and a servo pattern comprising a plurality of higher Hc, higher Mrt regions and a plurality of lower Hc, lower Mrt regions, wherein the servo pattern includes a plurality of regions extending in a radial direction across the data zone to divide the latter into a plurality of sectors.
Embodiments of the present invention include providing the apertured mask in the form of a patterned stencil or a photolithographically patterned resist layer.
In accordance with further embodiments of the present invention, the method further comprises the step of:
(d) initializing the servo-patterned magnetic medium by applying a unidirectional, high strength DC magnetic bias field to the magnetic layer to unidirectionally align the magnetization direction of each of the magnetic domains of the ion-implanted and non-implanted areas of the magnetic layer and then adjusting lowering the strength and reversing the direction of the DC magnetic bias field to selectively reverse the magnetization direction of each of the ion-implanted areas of the magnetic layer, for example, by utilizing an externally positioned, variable strength electromagnet or an externally positioned, movable permanent magnet for applying the unidirectional DC magnetic bias field.
Another aspect of the present invention is a servo-patterned magnetic recording medium, comprising:
a magnetic layer having a surface with substantially uniform topography, the magnetic layer including a data zone and a servo pattern, the servo pattern comprising:
(a) a first patterned plurality of regions of first, higher values of magnetic coercivity Hc and magnetic remanence-thickness product Mrt; and
(b) a second patterned plurality of implanted regions of second, lower values of Hc and Mrt; wherein the second, lower values of Hc and Mrt are sufficiently lower than the first, higher values of Hc and Mrt for permitting sensing enabling accurate positioning of a read/write transducer head in the data zone but sufficiently high for providing the medium with thermal stability, high amplitude of magnetic transition, and high signal-to-noise ratio.
In accordance with certain exemplary embodiments of the present invention, the first, higher values of Hc and Mrt are in the range from about 6,500 to about 10,000 Oe and in the range from about 0.55 to about 0.60 memu, respectively; and the second, lower values of Hc and Mrt are about 6,000 Oe and about 0.50 memu, respectively. According to other embodiments of the present invention, the first, higher values of Hc and Mrt are about 6,000 Oe and 0.50 memu, respectively; and the second, lower values of Hc and Mrt are about 4,000 Oe and 0.40 memu, respectively.
According to embodiments of the present invention, the servo pattern comprises a plurality of regions extending in a radial direction across the data zone for dividing the data zone into a plurality of sectors; and the data zone includes a plurality of substantially concentric, circumferentially extending data tracks, wherein the servo pattern comprises the regions of second, lower values of Hc and Mrt for denoting the beginning and end of each data track.
In accordance with particular embodiments of the present invention, each of the second patterned plurality of regions of second, lower values of Hc and Mrt comprises a portion of the magnetic layer including implanted nitrogen ions or implanted ions of at least one inert gas element having an atomic weight of at least 35, e.g., argon ions.
Still another aspect of the present invention is a magnetic recording medium comprising:
a magnetic layer having a surface with substantially uniform topography; and
means within said magnetic layer for providing a data zone and a servo pattern while affording said medium with thermal stability, high amplitude of magnetic transition, and high signal-to-noise ratio.
Additional advantages and aspects of the present invention will become apparent to those skilled in the art from the following detailed description, wherein embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as limitative.